With images an ever-growing proportion of what we share on social networks, Facebook fears that users with visual impairments may be missing out.

Beginning Tuesday, the company is tweaking its timelines so that users of screen readers can hear not just the text on a page, but also a brief description of what any images may contain. Until now, they’ve heard only the name of the person who posted the photo.

To describe the images, Facebook built a computer vision system with a neural network trained to recognize a number of concepts, including places and the presence of people and objects. It analyzes each image for the presence of different elements, and then composes a short sentence describing it that is included in the webpage as the “alt” text of the image.